1. Field of the Invention
The present invention pertains to the technical field of an internal combustion engine having an auxiliary combustion chamber, and more particularly, to a technique for controlling intensity of a torch flame directed from the auxiliary combustion chamber to a main combustion chamber.
2. Description of Related Art
In order to improve heat efficiency and exhaust performance of an internal combustion engine, a lean air/fuel mixture (also referred to as a “diluted mixture”) may be provided to the engine when it is operating at a relatively low engine load. In a related internal combustion engine, it is known to provide a main combustion chamber and an auxiliary combustion chamber. Such an internal combustion engine may also be referred to as an “auxiliary combustion chamber type internal combustion engine.” According to this related internal combustion engine, a torch flame (also referred to as a “flame jet”) is directed from the auxiliary combustion chamber to the main combustion chamber so as to promote the burning of a diluted mixture in the main combustion chamber.
According to the related internal combustion engine, an appropriate intensity torch flame may shorten a delay in igniting a mixture in the main combustion chamber, and may expand the engine operating conditions during which knocking is prevented. As it is used herein, the terms “knock” or “knocking,” also known as “pinging” or “detonation,” refers to when the air/fuel mixture in a combustion cylinder has been ignited, but smooth combustion is interrupted when an unburned mixture portion in the combustion chamber explodes before being reached by a flame front. The torch flame that is directed from the auxiliary combustion chamber according to the related internal combustion engine is fixed by, for example, the shape of the auxiliary combustion chamber. Thus, a problem with the related internal combustion engine is that it is not possible to optimize the torch flame for a given engine operation condition.
According to another related internal combustion engine, a torch flame impinges on a piston surface to cool the torch flame jet, thereby suppressing knocking. However, a problem according to this related internal combustion engine is increased engine cooling losses, i.e., energy lost due to heating of the engine structure, because the torch flame impinges on the piston surface. Moreover, in addition to deteriorated net heat efficiency, an appropriate intensity torch flame is not provided for a given engine operation condition.
Thus, it would be desirable to provide an auxiliary combustion chamber type internal combustion engine that does not suffer from the problems of the related art internal combustion engines. In particular, it would be desirable to provide an auxiliary combustion chamber type internal combustion engine with improved net heat efficiency and with an appropriate intensity torch flame for a given engine operating condition.